Magnification

Magnification is the ability of a telescope to make a small, distant object large enough to examine in detail. If you look at the Moon (250,000 miles away) with a 125 power (125x) telescope, it's essentially the same as looking at it with your bare eyes from 2000 miles away (250,000 ÷ 125 = 2000). The same telescope used terrestrially will make an object one mile away appear to be only 42 feet away (5280 feet ÷ 125 = 42).
The magnification of a telescope is determined by dividing the focal length of the telescope (usually in millimeters) by the focal length of the eyepiece used (again, usually in millimeters; but in all cases by the same unit of measurement used for the telescope focal length). For example, a 2000mm focal length telescope and a 10mm focal length eyepiece will give you a magnification of 200 power (2000 ÷ 10 = 200). The same 2000mm telescope with a 20mm eyepiece will give you 100x (2000 ÷ 20 = 100).


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